The hydrogen consumed by a fuel cell power plant may for example be generated by a fuel reforming system.
The fuel reforming system first generates fuel vapor by vaporizing a hydrocarbon fuel such as methanol or gasoline, and reforms the fuel vapor in the presence of a catalyst so as to generate reformate gas having hydrogen as its main component. However, as a considerable time is required from supply of liquid fuel to generation of reformate gas, the production amount of reformate gas cannot be controlled only by controlling the supply of liquid fuel.
Due to this delay, for example, unnecessary reformate gas may be generated when the power generation load of the power plant falls.
In this regard, JP 2001-10803 published by the Japanese Patent Office in 2001 discloses a branch pipe branching off from a fuel vapor supply pipe which connects the vaporizer and reformer. The branch pipe is connected to a fuel tank via a valve. When the fuel vapor amount required by the reformer falls due to a decrease of the power generation load etc., the valve is opened so that surplus fuel vapor is returned from the branch pipe to the fuel tank.